Syrian rebels have been fleeing into the Lebanese Sunni-dominated town of Arsal, which is surrounded by Shiite villages that are guarded by Hezbollah militants, since the rebel stronghold of Yabroud was recaptured by the Syrian military.

Lebanese troops have been seen patrolling the rugged, hilly border area.

The fall of Yabroud - a frontier town and a strategic smuggling hub for the rebels trying to overthrow Syria's president Bashar Assad - was a major gain for Syrian government troops and their Hezbollah allies.

It was also the Syrian opposition fighters' last stronghold in the vital border area. Assad's forces have now consolidated authority in Syria's major cities, including the capital, Damascus.

Yabroud fell into Syrian government hands after months of fighting in the mountainous Qalamoun region between Assad's forces and Hezbollah fighters on one side and rebel groups, mostly Islamist militant groups, on the other.

The Hezbollah fighters have been instrumental to Assad's success on the battlefield, and support from the Iranian-backed fighters appears to have tipped the balance into the government's favour in Yabroud.

However, with opposition fighters fleeing into Lebanon, where Hezbollah is a major force, the conflict is likely to spill into Syria's smaller neighbour. The civil war has already ignited polarising sectarian tensions between Lebanon's Sunnis and Shiites.

In the past weeks, Sunni militants have carried out several suicide bombings and car bomb attacks in Shiite dominated towns and suburbs of Beirut that are Hezbollah strongholds, claiming they were revenge for the Iran-backed group's role inside Syria.

A militant Sunni group has claimed responsibility for a car bombing in Nabi Othman, a predominantly Shiite town in Lebanon's Bekaa Valley that also has a significant Christian community.

The Nusra Front in Lebanon said in a statement posted on its Twitter account that the attack, in which two people were killed and 14 were wounded, was in revenge for Hezbollah's support for Assad and "a quick response" for the fall of Yabroud into Syrian government hands.

The statement also said the Nabi Othman bombing was in retaliation for Yabroud and because of Hezbollah's "bragging about it".

In footage broadcast live on state television in Damascus, Syrian army officers raised the national flag in Yabroud's main town square and covered rebel flag with posters praising Assad's troops.